Machine for continuous flash butt-welding of parts

ABSTRACT

A machine for continuous flash butt-welding in which a movable clamp automatic rate-of-travel control device for use during flashing comprises two a.c. to d.c. convertors, two potentiometers, two synchronized switches either of which might be set to two positions, an amplifier and a reversing electric motor coupled so that the above device regulates the ratio between the effective values of the electric voltage across the parts to be welded during the flashing operation and secondary voltage of a welding transformer at no-load.

United States Patent 1191 Lifshits et al. 1 Feb. 5, 1974 MACHINE FOR CONTINUOUS FLASH BUTT-WELDING OF PARTS [56] References Cited [76] Inventors: Viktor Senderovich Lifshits, UNITED STATES PATENTS Kavkazsky bulvar, 21 Korpus 2, kv. 3,548,144 12/1970 Riley 219/97 7 vhdimir Rubenovich 3,555,237 1 1971 Riley 219 97 Andrianov, pmezd Zarevy, 3, 3,681,563 8/1972 Lifshits 219/97 19; Nikolai Nikolaevich Rykalin, Ulitsa Akademika Gubkina, 4 kv. Primary Examiner-l Twhe 4; Tibor Ferentsevich Krasnev, Attorney, Agent, or Firm-Holman & Stern Slarokerpechny Pereulok 4, kv. l, all of Moscow; Nikolai Vasilievich ABSTRACT Podola, Kiev, ulitsa Pushkinskaya 8, A machine for continuous flash butt-welding in which kv. l2; Vadim Petrovich Krivonos, a movable clamp automatic rate-of-travel control de- Kiev, ulitsa Repina, l3, kv. 1, both vice for use during flashing comprises two a.c. to do. of Kiev, all of U.S.S.R. converters, two potentiometers, two synchronized [22] Filed July 10 1972 switches either of which might be set to two positions, an amplifier and a reversing electric motor coupled so [21] Appl. No.: 270,284 that the above device regulates the ratio between the effective values of the electric voltage across the parts [52], Us. Cl. I I 219 /97 to be welded during the flashing operation and secon- [51] Int. 11/04 dary voltage of a welding transformer at [58] Field of Search 219/97, 100 3 Claims, 2 Drawing Figures eon/ween)? 9 MACHINE FOR CONTINUOUS FLASH BUTT-WELDING OF PARTS BACKGROUND OF THE INVENTION The present invention relates to apparatus for welding workpieces and more particularly to machines for resistance butt-welding of parts by continuous flashing.

It is known to have machines for continuous flash butt-welding of parts which comprise a frame, a welding transformer with current-carrying conductors, a primary and a secondary winding, movable and stationary clamps for a workpiece to be welded coupled by conductors to the transformer secondary and located on the machine frame, a movable clamp travel gear, a movable clamp travel gear control element, a device for automatic control of the rate of travel of the movable clamp during flashing, referred to hereinafter as a movable clamp automatic rate-of-travel control device, and an actuating mechanism with a drive for the movable clamp automatic rate-of-travel control device with the above mechanism affecting the movable clamp travel gear control element during the flashing action.

A disadvantage of the conventional machines for flash butt-welding lies in that the flashing rate is essentially controlled in accordance with a stringent pre-set program which neglects the effect of random disturbing factors on stability and the thermal efficiency of the flashing process.

SUMMARY OF THE INVENTION The present invention has the principal object to develop a machine for the continuous flash butt-welding of parts so that it becomes possible to control the ratio between the effective values of electric voltages at the parts to be welded during the flashing operation, and the secondary voltage of a welding transformer at noload.

The essence of this invention consists in that in a machine for the continuous flash butt-welding of parts incorporating a frame, a welding transformer with conductors and a primary and a secondary mounted on the frame a movable and a stationary clamp for the workpiece coupled by the conductors to the transformer secondary, a movable clamp automatic rate-of-travel control device for use during flashing, and an actuator of the movable clamp automatic rate-of-travel control device affecting a movable clamp travel gear control element during the flashing operation according to the invention the movable clamp automatic rate-of-travel control device for use during flashing comprises two a.c. to d.c. convertors, two potentiometers, two synchronized two-way switches, an amplifier device and a reversing electric motor with the first a.c. to do convertor being connected to the primary of the welding transformer, the second convertor being shunted with the secondary of the welding transformer, the first potentiometer coupled to the output of the first convertor, the second potentiometer connected to the output of the first potentiometer and the switches connected in such a manner that when set to one position the amplifier input is connected in series with the outputs of the second convertor and the first potentiometer and the amplifier output is coupled to the reversing motor whose shaft is mechanically linked to a sliding contact of the first potentiometer and when the switches are shifted to another position the amplifier input is connected in series with the outputs of the second convertor and the second potentiometer and the amplifier output coupled to the actuator drive of the movable clamp automatic rate-of-travel control device used during flashing.

For the purpose of giving those skilled in the art a better understanding of the invention and a better appreciation of the advantages of this invention, a description of exemplary embodiments of the invention will be considred with reference to the appended drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a machine for the continuous flash butt-welding of parts according to the invention;

FIG. 2 is an elementary diagram of a movable clamp automatic rate-of-travel control device for use during flashing.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A machine for continuous flash butt-welding consists of a frame 1 (FIG. 1), transformer 2, movable clamp 3 and stationary clamp 4 for parts 5 to be welded mounted on frame 1. Movable clamp 3 and stationary clamp 4 for parts 5 being welded are connected to transformer 2 by means of conductors 6. Movable clamp 3 is shifted along frame 1 by travel gear 7 which may be in the form of a hydraulic cylinder. Travel gear 7 is governed by control element 8 made for instance in the form of a follow-up element such as a three-way slide valve with a rod. During flashing the inputs of movable clamp 3 automatic rate-of-travel control device 9 are coupled with the windings of transformer 2. Thus the output of device 9 is connected to the input of actuator 10 affecting control of element 8 during the flashing action.

Actuator 10 may be a screw pair whose screw acts on the rod of control element 8 and a nut is imparted a rotary motion by a variable-speed reversing motor incorporated in actuator 10.

An elementary diagram of movable clamp 3 automatic rate-of-travel control device 9 and its coupling with the welding transformer 2, parts 5 to be welded and actuator 10 is illustrated in FIG. 2.

In FIG. 2 device 9 is a block composed of two a.c. to d.c. convertors l1 and 12 with the input of convertor 11 connected to primary 13 of transformer 2 and that of convertor 12 to workpieces 5 in parallel with secondary 14 of transformer 2. Device 9 also comprises potentiometer 15 coupled to the output of convertor 11 and potentiometer 16 connected to the output of potentiometer 15. Switch 17 of device 9 is connected into the input circuit of amplifier 18 and switch 19 into the output circuit of amplifier 18 incorporated into device 9. With switches 17 and 19 set to position I the input of amplifier 18 is connected in series with the outputs of convertor 12 and potentiometer 15 while the output of amplifier 18 is coupled to reversing electric motor 20 whose shaft is mechanically linked to a sliding contact of potentiometer 15. With switches 17 and 19 shifted to position II the input of amplifier 18 is connected in series with the outputs of convertor l2 and potentiometer l6 and the output of amplifier 18 is coupled to variable-speed reversing electric motor 21 of actuator 10. I

The a.c. to d.c. convertors l1 and 12 may be for example, rectifiers or square-law detectors.

To perform the welding process on the machine according to the instant invention, a number of preliminary operations are carried out. These include: the setting of secondary voltage E with transformer 2 at noload; the gripping of parts to be welded in movable clamp 3 and stationary clamp 4; setting initial rate V of travel of movable clamp 3 during flashing and upset rate V,,; timing the beginning of the upset operation t, and its value 1; memorizing the value of the secondary voltage of the transformer under no-load condition and setting the ratio between secondary voltages E of the transformer during the flashing process and E at no-load.

With transformer 2 at no-load the secondary voltage E is set by means of a switch (not shown in FIG. 2) connected into primary 13 of welding transformer 2. Initial flashing rate V, is set manually with the aid of control element 8. Time t, at which upsetting is initiated and its value 1 are determined by setters not shown in the drawing. Upset ratio V is set by a reducing the valve incorporated in a hydraulic system which serves to feed gear 7 (hydraulic cylinder).

Ratio E /E between the secondary voltages of the transformer during flashing and at no-load is set by shifting the sliding contact of potentiometer 16 to a position in which the ratio between the output and input voltages of the potentiometer is equal to the pre-set ratio 13 /15 between the secondary transformer voltages.

As soon as the foregoing preliminary operations are completed, welding transformer 2 is energized and memorizing of the secondary voltage of the transformer at no-load, is effected. To attain this switches 17 and 19 are set for a short interval to position I to be then returned to position ll.

When switches 17 and 19 are set to position I theoutput voltage U of converter 12 which is proportional to the secondary voltage E of the transformer and the output voltage U of the potentiometer 15 which is proportional to the transformer supply voltage E are connected in series opposition to the input of amplifier 18.

Voltage difference A U U U is gained by amplifier 18 which transmits a signal to set the reversing motor 20 in rotation which is linked mechanically with the sliding contact of potentiometer 15. The direction of rotation of the motor 20 is chosen so that the sliding contact of potentiometer 15 will move in such a direction and until voltage difference A U is equal to zero with an accuracy conditioned by the sensitivity threshold of amplifier 18. Hence with motor 20 in equilibrium Since in performing the memorize operation the welding transformer is practically at no-load, its secondary circuit will be exposed to the action of no-load voltage E through which voltages U and U are proportional to E therefore where K is a conversion factor of convertor 12.

After the reversing motor 20 has attained a balanced state switches 17 and 19 are shifted from position 1 to position ll. Control winding 22 of motor 20 will be deenergized and will fix the position of the sliding contact of potentiometer 15, hence providing memorization of the value of output voltage U, of the potentiometer which is proportional to secondary voltage E of the transformer at no-load.

Simultaneously the output voltage U of convertor l2 and the output voltage U of potentiometer 16 which is a fraction of output voltage U. of potentiometer 15 are fed to the input circuit of amplifier 18 in series opposition when the switches 17 and 19 are in position lI. Hence, u

where a U /U (R/R,,) s l and is a factor equal to the ratio between the output resistance R of potentiometer 16 and its total resistance R voltage difference which exists in the input circuit of amplifier 18 is gained by the amplifier and sets in rotation the motor 21 of the actuator 10 which affects with the aid of control element 8, travel gear 7 change the rate of travel of movable clamp 3 together with a workpiece 5 towards stationary clamp 4.

After workpieces 5 have come in contact the secondary circuit of transformer 2 it is energized and the process of flashing is initiated.

Current value in the secondary circuit of transformer 2 depends on the rate of bringing together the parts 5 which are being welded together: the higher the rate the heavier will be the current.

Flow of current in the secondary circuit of transformer 2 is accompanied by a drop in secondary voltage E applied at the input of convertor 12 which is clue to a voltage drop across the internal resistance of transformer 2. Consequently when the rate of bringing parts 5 together to be welded increases, secondary voltage E of transformer 2 decreases.

Apparently the rate of drawing parts 5 together will vary until the secondary voltage E of transformer 2 attains the value at which output voltage U of converter 12 is equal to output voltage U, of potentiometer 16. Hence U U or K E ozU ctK E wherefrom I E /E a const.

Hence on the machine in question the movable clamp automatic rate-of-travel control device (for use during flashing) assures stabilization of the ratio between the voltage E across the secondary circuit of transformer 2 during the flashing action and no-load voltage E of the circuit.

Voltage ratio E /E is unambiguously related to the ratio between power take-off by parts 5 being welded during flashing and maximum rating of transformer 2.

As the limitation of the transformer take-off power to a value not in excess of the transformer rating is a factor of vital importance for stabilizing the flashing operation in the resistance butt welding of parts, the use of the machine of the instant invention will ensure a more stable and efficient flashing action.

What is claimed is:

1. A machine for continuous flash butt-welding of parts, incorporating: a frame; a movable clamp and a stationary clamp disposed on said frame for gripping the parts to be welded; a welding transformer having conductors, a primary winding and a secondary winding, also mounted on said frame; travel gear means for shifting said movable clamp during the flashing operation; control means of said travel gear means; actuator means for actuating said control means during flashing; means for automatically controlling the rate of travel of said movable clamp said means including; a first ac. to (L0. convertor the input of said convertor being connected to said transformer primary winding; 21 second ac. to do convertor connected in parallel with said transformer secondary winding; a first potentiometer coupled to the output of said first convertor; a second potentiometer connected to the output of said first potentiometer; two switches operating synchronously each of said switches being operable between two positions; an amplifier having an input and an output; a reversing electric motor having a shaft connected to a sliding contact of said first potentiometer so that when said switches are set to the first of said positions the input of said amplifier is connected to the outputs of said second convertor and of said first potentiometer, the output of the amplifier being coupled to said reversing electric motor and when said switches are set to the second of said positions the input of said amplifier is connected in series to the outputs of said second convertor and of said second potentiometer, the output of said amplifier being coupled to the input of said actuator of said automatic control device.

2. A machine for continuous flash butt-welding of parts comprising:

frame means having a movable clamp and a stationary clamp mounted thereon for respectively gripping the parts to be welded;

a welding transformer mounted on said frame means and having a primary and secondary circuit, said secondary circuit having conductors connected to each of said parts to be welded;

travel gear means for moving said movable clamp during a flashing operation;

control means of said travel gear means and operably connected therewith;

actuator means for actuating said control means dur ing flashing;

means for automatically controlling the rate of movement of said movable clamp and connected between said welding transformer and said actuator means, said means operating to ensure that the ratio of the voltage across said secondary circuit of said welding transformer and thus across said parts during flashing, and the voltage across said secondary citcuit at no-load of said welding transformer, is a constant.

3. A machine as claimed in claim 2 wherein said means for automatically controlling the rate of movement of said movable clamp includes; first and second ac. to do. convertors each having an input and an output, the input of said first convertor being connected to said primary circuit of the welding transformer; said second convertor being connected in parallel with said secondary circuit of said welding transformer; first and second potentiometers each having an input and an output and slidable contacts, aid first potentiometer being coupled to the output of said first convertor, said second potentiometer being connected to the output of said first potentiometer; a first and second switch means operating synchronously, each of said switch means being operable between two positions; an amplifier having an input and an output; reversing electric motor means having a shaft which is operatively connected with the sliding contact of said first potentiometer, so that when said first and second switch means are set to the first of said-two positions the input of said amplifier is connected to the output of said second convertor and the output'of said amplifier is coupled to said reversing electric motor means, and said amplifier output generates a voltage difference between the output of said first potentiometer and the output of said second convertor, said voltage difference operably causing said reversible electric motor means to move the contact of said first potentiometer until said voltage difference is zero, and when said first and second switch means are set to the second of said two positionsthe input of said amplifier is connected in series to the output of said second convertor and the output of said amplifier is coupled to the input of said actuator means to thereby control the rate of movement of said movable, clamp, said amplifier output generating a voltage difference between the output of said second convertor and the output of said second potentiometer which difference attains zero during the flashing process to a stabilization condition of operation when the ratio of the voltage across said secondary circuit, and thus across said parts to be welded, and the voltage across said secondary circuit at no-load is a constant. 

1. A machine for continuous flash butt-welding of parts, incorporating: a frame; a movable clamp and a stationary clamp disposed on said frame for gripping the parts to be welded; a welding transformer having conductors, a primary winding and a secondary winding, also mounted on said frame; travel gear means for shifting said movable clamp during the flashing operation; control means of said travel gear means; actuator means for actuating said control means during flashing; means for automatically controlling the rate of travel of said movable clamp said means including; a first a.c. to d.c. convertor the input of said convertor being connected to said transformer primary winding; a second a.c. to d.c. convertor connected in parallel with said transformer secondary winding; a first potentiometer coupled to the output of said first convertor; a second potentiometer connected to the output of said first potentiometer; two switches operating synchronously each of said switches being operable between two positions; an amplifier having an input and an output; a reversing electric motor having a shaft connected to a sliding contact of said first potentiometer so that when said switches are set to the first of said positions the input of said amplifier is connected to the outputs of said second convertor and of said first potentiometer, the output of the amplifier being coupled to said reversing electric motor and when said switches are set to the second of said positions the input of said amplifier is connected in series to the outputs of said second convErtor and of said second potentiometer, the output of said amplifier being coupled to the input of said actuator of said automatic control device.
 2. A machine for continuous flash butt-welding of parts comprising: frame means having a movable clamp and a stationary clamp mounted thereon for respectively gripping the parts to be welded; a welding transformer mounted on said frame means and having a primary and secondary circuit, said secondary circuit having conductors connected to each of said parts to be welded; travel gear means for moving said movable clamp during a flashing operation; control means of said travel gear means and operably connected therewith; actuator means for actuating said control means during flashing; means for automatically controlling the rate of movement of said movable clamp and connected between said welding transformer and said actuator means, said means operating to ensure that the ratio of the voltage across said secondary circuit of said welding transformer and thus across said parts during flashing, and the voltage across said secondary citcuit at no-load of said welding transformer, is a constant.
 3. A machine as claimed in claim 2 wherein said means for automatically controlling the rate of movement of said movable clamp includes; first and second a.c. to d.c. convertors each having an input and an output, the input of said first convertor being connected to said primary circuit of the welding transformer; said second convertor being connected in parallel with said secondary circuit of said welding transformer; first and second potentiometers each having an input and an output and slidable contacts, aid first potentiometer being coupled to the output of said first convertor, said second potentiometer being connected to the output of said first potentiometer; a first and second switch means operating synchronously, each of said switch means being operable between two positions; an amplifier having an input and an output; reversing electric motor means having a shaft which is operatively connected with the sliding contact of said first potentiometer, so that when said first and second switch means are set to the first of said two positions the input of said amplifier is connected to the output of said second convertor and the output of said amplifier is coupled to said reversing electric motor means, and said amplifier output generates a voltage difference between the output of said first potentiometer and the output of said second convertor, said voltage difference operably causing said reversible electric motor means to move the contact of said first potentiometer until said voltage difference is zero, and when said first and second switch means are set to the second of said two positions the input of said amplifier is connected in series to the output of said second convertor and the output of said amplifier is coupled to the input of said actuator means to thereby control the rate of movement of said movable clamp, said amplifier output generating a voltage difference between the output of said second convertor and the output of said second potentiometer which difference attains zero during the flashing process to a stabilization condition of operation when the ratio of the voltage across said secondary circuit, and thus across said parts to be welded, and the voltage across said secondary circuit at no-load is a constant. 